Gun Violence Might Have Infectious Effect

"Based on this study's results, showing the importance of personal contact with violence, the best model for violence may be that of a socially infectious disease," says Felton Earls, MD, HMS professor of social medicine and principal investigator of the study and of the the Project on Human Development in Chicago Neighbourhoods.

"Preventing one violent crime may prevent a downstream cascade of 'infections'. And the lessons learned in Chicago should be broadly applicable. Generalising this to any large city should be valid," Earls said.

The study, a five-year project that included interviews of over 1,500 children and teenagers from 78 Chicago neighbourhoods, used statistical advances and extremely detailed information about the study subjects to go beyond the correlations and associations typically used by social scientists to determine violent behaviour. "We have a broad range of factors, and a long course of study, so we can tease out the causal mechanisms," said first author Jeffrey Bingenheimer, doctoral candidate at the University of Michigan.

The researchers studied the subject teens at three points in their adolescence. Initially they and their caregivers were intensively interviewed and data was collected about their families, personalities, neighbourhoods, school performance, and many other factors. Two years later, the subjects were interviewed to see which of them had actually seen someone being shot, or shot at. Finally, almost three years further on, they were interviewed again to determine who had participated in gang violence or other violent actions.

After finding that witnessing violence more than doubled the risk that teens would violently offend, the team looked at their statistics to check whether an unknown factor could be hiding from them. "And honestly, it's very difficult to think what we might have left out," Earls said, pointing to the 153 variables that were embraced in the study.